Oystercatchers eating mussels were aggressive and often stole mussels from each other. A stable and linear dominance hierarchy existed amongst 10 birds studied in detail. The intake rates of 6 out of 8 birds decreased with increasing densities of oystercatchers, but this did not happen in the 2 top-dominant individuals. Interference in subdominants was due to increased intraspecific kleptoparasitism, to decreased capture rates probably caused by avoidance, and, perhaps, to increased time spent in aggression. Subdominants avoided high densities of conspecifics, but they did not stop feeding when high densities occurred. Data may be explained in terms of increased opportunities for dominants to steal food from subdominants at high bird densities. Competition for small-scale feeding sites may also have been important. The dispersion of oystercatchers over the mussel bed can be described by a modification of the 'ideal despotic distribution' proposed by Fretwell (1972).-from Authors